Codominance and Sex-linked traits

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Codominance and Sex-linked traits
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CODOMINANCE

• 2 alleles are dominant and both are expressed

Most common examples are blood type and flower
color.
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Blood Type

• 3 possible alleles A, B, O
• 4 possible PHENOTYPES
• A AB B O

Both alleles A and B are dominant. When both A
and B alleles are present, they are both
expressed.
Type O is recessive.
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Blood Type

• There are multiple genotypes
• Phenotype A Genotype AA, Ao
• Phenotype B Genotype BB. Bo
• Phenotype AB Genotype AB
• Phenotype O Genotype oo

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Blood Type

• Punnett Squares are worked the same way as
  before
• Cross AA with Bo

A
A
AB
AB
B
What are the possible Genotypes? Phenotypes?
o
Ao
Ao
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Sex-linked traits

• Sex is determined by the X and Y chromosomes.

XX is female XY is male
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Sex-linked traits

• Genotype uses Xs and Ys.
• Female XX Male XY

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Sex-linked traits

• Cross a male and a female.
• What are the frequencies of
• female offspring? Male offspring?

X
X
XX
X
XX
Y
XY
XY
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Sex-linked traits

• Some genes are only found on the
• X or the Y chromosome. These traits are
  SEX-LINKED.
• Common examples include Hemophilia and
  colr-blindness.

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Sex-linked traits

• The alleles you are looking at are written as
  superscripts on the X and Y chromosomes.
• XBXB XBY

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Sex-linked traits

• Example The gene for colorblindess is only found
  on the X chromosome
• B normal vision b colorblind
• Female with normal vision XBXb or XBXB
• Female with colorblindness XbXb
• Male with normal vision XBY
• Male with colorblindness XbY

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Sex-linked traits

• Punnett squares work the same way, use X and Y in
  the genotypes.

XB
Xb
Cross a heterozygous normal vision female with a
normal vision male. Genotypes? Phenotypes?
XB
XBXB
XBXb
XBY
Y
XbY